Technical Field
The present disclosure relates to local interconnect networks (LIN) and, particularly, to local interconnect network receivers.
Description of the Related Art
The Local Interconnect Network (LIN) is a serial network protocol used for communicating between components in vehicles. It is defined as a time-triggered, master-slave network, eliminating the need for arbitration among simultaneously reporting devices. It is implemented using a single wire communications bus, which reduces wiring and harness requirements and thus helps save weight, space and cost.
Defined specifically for low-cost implementation of vehicle sub-network applications by the LIN Consortium, the LIN protocol achieves significant cost reduction since it is fairly simple and operates via an asynchronous serial interface (UART/SCI), and the slave nodes are self-synchronizing and can use an on-chip RC oscillator instead of crystals or ceramic resonators.
In order to maintain total current consumption in a LIN network at acceptable levels, increasing the number of slave nodes in a LIN network requires lower and lower current consumption for each of the nodes.
LIN network operational modes include an active mode with full receiving and transmitting capability; a silent (low-power) mode, in which full receiving capability, but no transmitting capability, is provided; and a sleep (power-down) mode, in which only waking-up capability is enabled. Current consumption in silent mode is about 50 microamps, while that in sleep mode is about 5-10 microamps. Thus, a consumer needing only receiving capability has to operate in silent mode, consuming 50 microamps.
Usually, the silent mode and the sleep mode functionality are implemented using distinct dedicated blocs in a given integrated circuit.
In particular, LIN bus signaling thresholds for “dominant” (logic low) and “recessive” (logic high) levels are centered on half the battery voltage (Vbat/2), with a 0.1 Vbat hysteresis typically required. That is, the recessive-to-dominant threshold is approximately 0.45*Vbat, while the dominant-to-recessive threshold is approximately 0.55*Vbat. Consequently, a window comparator is required to identify bus signals. However, Vbat can range from 6-30 V, which requires wide common mode range compliance for a window comparator. That is, Vbat/2 (and the LIN signal) voltages can dramatically exceed the input voltage range of a window comparator during voltage modes (i.e., silent and operational). As a consequence, matched voltage dividers are commonly used to generate matched fractions of the Vbat/2 and LIN voltages that stay within the input voltage range of the window comparator.
Because significant overhead (a voltage regulator, external bias, etc.) around the voltage mode window comparator is required, overall current consumption of the LIN receiver in voltage mode exceeds requirements during sleep mode. Thus, the voltage mode LIN receiver comparator cannot be used as the wake circuit comparator.
In order to save power during sleep mode, the wake circuit comparator typically compares the LIN bus voltage to a transistor Vt (threshold voltage) or a sum of transistors Vt. This results in a very simple and low-power circuit, but on the other hand, it requires as well a constant detection level, in the range of 3.5-4V, rather than the standard half battery voltage Vbat/2. Thus the wake circuit cannot be used for receiving bus data.